Invincible:
This brightly colored universe would totally lend itself to a action video game. Basically, Invincible has the powers of Superman, so it would totally lend itself to a cel-shaded sandbox superhero game.

Walking Dead:
Think a more serious version of Dead Rising with squad mechanics and more linear gameplay.

Marvel Zombies:
Play as your favorite zombie and battle your way to the end of life in the galaxy.

Y: The Last Man:
Keep your identity secret as you try to collect all the materials to help save humanity from extinction. Also, tons of sex mini-games.

Gantz:
This manga was created to be a video game. Crazy epic enemies, a obvious increase in monster difficulty and weapons, and a crazy-ass story line and characters to keep things interesting. As far as I know, no game has been made yet, but I think an american developer should pick this up and make it before some Japanese developer makes a shitty FPS out of it.